Invalid Certificate Error: What You Need to Know to Fix It

An invalid certificate error occurs when a website’s SSL/TLS certificate does not match the domain name. This can happen due to expired, misconfigured, or self-signed certificates. To resolve, check SSL settings, verify the origin server’s certificate, and ensure proper DNS and HTTPS records.

Understanding Invalid Certificate Errors
An invalid certificate error is a common issue that can prevent users from accessing a website securely. This error occurs when the SSL/TLS certificate presented by the server does not match the domain name in the URL. Here are the key points to understand and resolve this issue:

1. SSL/TLS Certificate Requirements:
   The certificate must not be expired.

It must be issued by a trusted Certificate Authority (CA).
The domain name in the URL must match the certificate’s “Common Name” (CN) or “Subject Alternative Name” (SAN).
2. Causes of the Error:
Misconfigured Certificates: Using the wrong SSL mode in Cloudflare or incorrect settings can lead to mismatches.

Expired or Revoked Certificates: Certificates that are expired or revoked can cause browsers to display a mismatch error.
Self-Signed Certificates: Using self-signed certificates without proper validation can also result in mismatches.
3. Resolving the Issue:
Check Cloudflare SSL Settings: Ensure the correct SSL mode is selected in the Cloudflare dashboard.

Verify the Certificate on the Origin Server: Ensure the certificate’s CN or SAN matches the domain and is issued by a trusted CA.
Use Cloudflare’s Universal SSL: Enable Universal SSL in Cloudflare to ensure a valid certificate is provided.
Purge Cloudflare Cache: Clear the cache to update any outdated certificates.
Check for CNAME Cross-User Issues: Ensure DNS settings are correctly configured to avoid cross-user issues.
Re-issue or Renew SSL Certificates: If necessary, re-issue or renew the SSL certificate to ensure it includes the correct CN and all SANs.
By following these steps, you can diagnose and resolve invalid certificate errors, ensuring a secure and seamless user experience.

1. What causes an invalid certificate error?
   An invalid certificate error occurs due to expired, misconfigured, or self-signed certificates.
2. How do I check my SSL settings in Cloudflare?
   Log in to the Cloudflare dashboard, go to SSL/TLS settings, and select the appropriate SSL mode for your setup.

3. What is the difference between Full SSL and Full (Strict) SSL in Cloudflare?
   Full SSL uses the origin server’s certificate if it is installed but not fully validated. Full (Strict) SSL requires both Cloudflare and the origin server to have valid, matching SSL certificates.

4. How do I verify the certificate on the origin server?
   Ensure the certificate’s CN or SAN matches the domain and confirm it is issued by a trusted CA and not expired or revoked.

5. What tools can I use to analyze SSL certificates?
   Use tools like SSL Labs’ SSL Test or “What’s My Chain Cert” to analyze SSL certificates and identify mismatch issues.

Invalid certificate errors can be frustrating but are often easily resolved by checking and configuring SSL settings, verifying the origin server’s certificate, and ensuring proper DNS and HTTPS records. By following these steps, you can ensure a secure and seamless user experience.